Technology

Product Review: Green Masonry

A look at bricks, pavers, permeable pavers, and structural ‘blocks’ for green building.

When it comes to building materials, masonry is about as elemental as it gets. Available in many forms, from adobe to terra-cotta to brick and concrete, masonry products are typically cost-efficient, extremely durable, and recyclable. Much of the material that goes into these products is naturally abundant. In fact, most masonry building products are entirely natural, consisting of little more than earth itself—namely clay, silica, and other materials.

Based on this, one might think that masonry is the most environmentally acceptable type of building material, but this is not necessarily true. The raw materials must be excavated or mined, which can be ecologically disruptive. Because masonry is inherently heavy, the cost of transporting it from manufacturing plant to building site, and the fuel burned as a result, can be higher than for competing materials. And despite its basic earthen makeup, some amount of processing, along with considerable heat for cement and kiln-fired masonry, is typically required to transform the raw materials into finished products. These efforts can require significant energy consumption and produce carbon dioxide and other environmentally harmful by-products.

Manufacturers and associations representing masonry products defend their green building value, saying that the raw materials are generally available in most locations and easily obtainable with limited environmental impact. Proponents also cite the sustainability of masonry compared with other building materials, and they note that, after manufacture, the products are inert and can be ground up for use as clean fill or recycled into other masonry products. These claims are supported by the fact that masonry building products contribute toward green building credits in LEED, National Green Building Standard, and other programs.

Improvements to masonry products have been developed to reduce the environmental impact of manufacturing and transportation, improve the materials’ insulating properties, and increase their overall green building value. Innovations such as autoclaved aerated concrete, using fly ash and industrial waste as binders, and even returning to pre-industrial products and production methods (like adobe) are just a few of the alternatives available to builders.

Masonry manufacturers are also striving to meet the challenges of increasingly demanding energy codes, green building standards, and industry initiatives like the 2030 Challenge for Products, a new program that has set carbon-metric goals that include a 50% reduction in the “carbon footprint” of building materials by the year 2030.

Here’s a rundown of considerations to keep in mind when evaluating masonry products:

Adobe is perhaps the most basic masonry block. This prototypical “mud” brick has been used in construction throughout the world since the beginning of recorded time. It is manufactured and used here in limited applications, primarily in the American Southwest, due mainly to its indigenous architectural value. Although it can be made locally from almost any common soil mixed with a small amount of binder, such as straw or even animal dung, manufacturers today add stabilizers, including Portland cement and asphalt emulsion, to provide consistency and strength. Traditionally, adobe is made at the building site, sun-dried and stacked without mortar, then parged with a thick stucco coating, all of which adds to its energy-saving, environmental, and economical credit. However, it is less durable and more difficult to transport than other masonry products, and suitable mainly for structures in areas with low humidity and little rainfall.

Brick is a similarly ancient building block composed primarily of clay and silica. But because brick is baked or “fired” in a kiln, it is transformed into an extremely hard, durable ceramic material that resists erosion from water and wear. Various materials like lime, iron oxides, and magnesium, along with colorants, can be added during manufacture to impart a range of desired qualities, such as hardness, density, appearance, and uniformity. As with adobe, brick has distinct environmental attributes, including sustainability and recyclability, and the fact that its basic materials are locally or regionally sourced. However, the prolonged heat required to fire it and the energy used to transport its considerable bulk weigh against it as a green building material (according to one source, transporting brick for just 10 miles via horse cart in 18th century England could more than double its price).

Terra-cotta (Latin for baked earth) is another contemporary “all-natural” building product rooted in history. A ceramic, clay-based material much like brick, it is typically baked into tiles for use in flooring, roofing, and exterior cladding. In modern construction, terra-cotta is often used for rain-screen systems or ornamental embellishment on commercial buildings. It is commonly used as a structural building block in Europe and elsewhere, but not in the United States. Terra-cotta products used here are typically imported, so transportation weight, bulk, and cost are factors that limit its green building value, along with the heat energy and carbon dioxide generated in its production.

Concrete blocks and pavers, along with clay brick, are the most widely used structural masonry products in the United States and perhaps the world. Concrete is relatively inexpensive, can be mixed on-site or locally sourced and formed into virtually any shape, and, although it is easily recycled, it is as close to indestructible as any man-made building material ever produced. On the downside, the key ingredient in concrete is Portland cement, a manufactured material with high embodied-energy content. According to the Portland Cement Association, the industry has worked diligently to improve this process, and since 1972 has reduced energy consumption and fuel CO2 emissions in manufacturing by more than 37%. The association claims that cement production today “accounts for less than 3% of all U.S. industrial CO2 emissions, well below other sources” such as the petroleum, chemical, and iron and steel industries.

Over the years, substitute binder materials have been developed to reduce or eliminate Portland cement in concrete, such as industrial by-products like fly ash, steel slag, agricultural waste, and recycled post-consumer waste. New types of products have been created as well, such as pervious concrete pavers, which allow rain and groundwater to naturally drain into the soil through patios and parking areas. Autoclaved aerated concrete (AAC) is another innovation with green building benefits—precast blocks are resource-efficient, lightweight, and thermally insulating. However, AAC has only half the compressive strength of standard concrete, and, because it is porous and relatively soft, it must be parge-coated or enclosed to prevent deterioration.

The bottom line in all this is that most structural masonry products will contribute to green building credits simply because of their inherent sustainability, but builders can improve the performance, quality, and desirability of a structure by choosing masonry units that offer additional benefits such as resource efficiency, reduced weight, insulating value, recycled content, and other environmental attributes whenever possible. Masonry has always been an intrinsic part of residential construction. The innovations available in today’s materials just make it better.

Michael Morris, a former carpenter and builder, reports on construction topics as an EcoHome contributing editor.